Turn indicator switches serve for actuating a turn indicator, also known as a “blinker.” In the case of two-track motor vehicles with a steering wheel, said turn indicator switches are generally designed as steering column switches. Steering column switches serve in general for convenient and safe operation of the frequently required functions of a vehicle. They involve devices having at least one lever which acts on a switch connected thereto. The desired function can be implemented by manipulation of the lever.
In order to ensure easy reachability, steering column switches are generally arranged in the region of the vehicle driver. It is preferred in this case for said steering column switches to be fastened to the steering column of the vehicle between the dashboard and steering wheel. In this position, turn indicator switches are frequently combined with additional steering column switches which are used, for example, for actuating a windscreen wiper or a control device for the speed of the vehicle (cruise control).
In the inoperative (OFF) position of the turn indicator switch, the lever thereof is in a substantially horizontal starting position. The lever can be deflected, when required, from said starting position into at least one of two generally opposite switching positions to activate the turn indicator in the desired direction. Toward the end position of the range of movement, the lever is mechanically locked in the respective switching position thereof. In order to subsequently deactivate (switch OFF) the turn indicator, the latching of the lever can be released either manually or mechanically by rotation of the steering wheel.
Since the turn indicator generally serves for indicating an imminent or current turn direction, turn indicator switches are coupled to the steering angle of the steering wheel. This permits automatic resetting (to OFF) of the lever by moving out of the turn. The resetting takes place mechanically. For this purpose, the turn indicator switch contains an adjustment ring which is coupled to the steering wheel and in which a latching device can at least partially engage. As soon as the anticipated wheel angle has taken place, the resetting of the steering wheel is used in order to release the latching engagement by means of the co-rotating adjustment ring. As a result, the lever jumps back out of the deflected switching position thereof into the starting position and the turn of travel indicator is deactivated.
In the event of small steering movements, the movement angle of the adjustment ring may not suffice in order to release the latching device from the switching position.
To this end, DE 10 2006 052 108 A1 proposes a dynamically resettable turn indicator switch. The turn indicator switch comprises a lever which can be deflected from a starting position into two opposite switching positions. Furthermore, a latching device with a latching pin which, in particular in the respective switching position, reaches into the depression in an adjustment ring is provided. By this means, the turn indicator switch can be operated in a customary manner and coupled to the steering angle of the steering wheel. In order then to permit dynamic resetting of the turn indicator switch, additional magnetic actuation of the latching device is provided. For this purpose, the latching pin is formed from metal and is surrounded by a coil. After a defined interval from latching of the lever, an electrical current is temporarily conducted through the coil. Owing to the magnetic field building up, the latching pin is retracted, as a result of which the latching of the lever is released. As a result, the lever jumps back into the starting position thereof and the turn of travel indicator is deactivated.
The magnetically actuable latching device enables resetting of the lever, which resetting can also take place independently of the respective steering angle of the steering wheel. In this manner, for example, drivers of other vehicles are not irritated by a turn indicator which is active without reason, or even obstructed in guiding of their own vehicle.
More recent developments of steering systems provide dynamically variable ratio steering through which the handling of the vehicle is intended to be improved. The turn angle of the steerable road wheels can be changed here independently of the respective steering wheel angle. In other words, systems of this type no longer provide the customary linear transmission of the rotation of the steering wheel to the turning of the coupled wheels, but rather change the ratio of transmission dynamically depending on the respective driving situation. For example, in a parking situation, the wheel angle of the wheels can be significantly increased in relation to the specification via the steering wheel (high ratio) in order to permit maneuvering of the vehicle with as little steering effort as possible. In this manner, tight driving maneuvers can be undertaken with just a small rotation of the steering wheel without having to change grip thereon. By contrast, the stability at high speeds can also be improved by this means by the transmission converting only a small part of a possible steering movement into a wheel angle of the coupled wheels (low ratio).
Since, by this means, there is no longer any linearity between the steering angle at the steering wheel and the actual wheel angle of the coupled road wheels, this has direct effects on the relevant resetting of the turn indicator switch. In view of the turn indicator switches coupled as before mechanically to the steering wheel, the design and the operation of such a turn indicator switch therefore still leave space for improvements, in particular with regard to future steering systems.